The heath effects of occupational solvent exposure don’t always fade with time. A new study has found that years — sometimes even decades — down the road from their last workplace exposure, some workers are still experiencing very real cognitive impairments.

“Cognitive problems are pretty common at older ages and even though they are really common, we don’t know much about what causes them or how to prevent them,” said study co-author Erika Sabbath, a research fellow at Harvard School of Public Health. “There’s a large body of evidence that solvents are this group of occupational chemicals that have impacts on cognitive health in the short and medium term, but most studies are looking at groups that are still working. We wanted to know if (the impacts) would persist even after workers retired.”

Published in the May issue of Neurology, the study found that high exposure to solvents was significantly associated with cognitive problems, with the greatest risk found among retired workers who experienced a high lifetime exposure and whose last exposure was 12 to 30 years before taking part in the study. To conduct the study, researchers pulled from data on a socioeconomically diverse sample of more than 20,600 French workers employed at a national utility company, eventually conducting analyses on 2,143 retired men. Solvent exposure was categorized into four categories — chlorinated solvents, petroleum solvents, benzene and nonbenzene aromatic solvents — and workers were tested on cognitive functions such as verbal memory, verbal fluency, concentration and visual-motor speed. The study found that while time may heal cognitive impairments among workers who experienced moderate solvent exposure, workers with higher exposures are often not so lucky.

Solvents, such as glues, adhesives, paints and degreasers, are fairly common in the workplace and can find their way into the hands of a variety of workers. For example, benzene is used to make plastics and other synthetic materials, chlorinated solvents are used in dry cleaning solutions, and petroleum solvents are in furniture polishes and paints. The Neurology study included a cross-section of workers from the French utility company — those who worked at a desk, in the field and in the factory.

Of the study participants, 26 percent were exposed to benzene, 33 percent to chlorinated solvents and 25 percent to petroleum solvents. Participants, whose average age was 66 and average time since initial retirement was 10 years, took eight cognitive tests that evaluate thinking and memory skills. The results found that 59 percent had impaired scores on one to three of the tests; 23 percent had impaired scores on four or more tests; and 18 percent had no impaired scores. Sabbath told me that even after researchers adjusted for confounding variables and other health conditions, such as educational attainment and hypertension, they still found an association between solvent exposure and cognitive impairment.

“We feel like this is a strong association that didn’t go away when we adjusted for alternative explanations,” she said.

Overall, the study found “consistent associations” between occupational solvent exposure and a risk of impaired general cognitive status, psychomotor speed (physical skills such as coordination), semantic fluency, immediate recall and executive function. Risk of developing impairment was significantly linked with high exposure to chlorinated and petroleum solvents. Not surprisingly, those who experienced high levels of recent exposure were at greatest risk; however, researchers also found that workers who were exposed up to 50 years prior were also experiencing cognitive issues.

“That finding was really surprising,” Sabbath said. “The idea that these effects kind of fade away has sort of been the prevailing thought…but in highly exposed workers, the effect didn’t fade the way the literature may have suggested.”

Sabbath and her co-authors — Laure-Anne Gutierrez, Cassandra Okechukwu, Archana Singh-Manoux, Helene Amieva, Marcel Goldberg, Marie Zins and Claudine Berr — note that their findings have “particular importance in the present context of rising retirement ages in industrialized countries. …Organizations, payers and society may benefit from both a more productive workforce and a reduction in workers’ postretirement health care costs by protecting them from adverse exposures.” Sabbath told me that it’s hard to say whether the study results are applicable to the U.S., as they can’t say for sure if the French solvent exposures were within the U.S. Occupational Safety and Health Administration’s maximum exposure standard. But she noted that previous research has found adverse health effects even within the current OSHA exposure standard.

“That’s the next question we have to ask,” Sabbath told me. “Is it possible that our current standard isn’t enough to fully protect workers against negative health effects?”

Of course, it’s also a situation in which there’s really no downside to prevention, Sabbath noted. For example, she said, supplying and training workers on properly using respirators, providing good ventilation or eliminating worker exposure completely by choosing alternative materials could go a long way toward protecting cognitive health. Clinicians can also use the study findings to screen for and intervene on cognitive impairments early on if they know to ask about a patient’s occupational exposure to solvents. Interestingly, Sabbath told me that her previous research has found that education seems to be protective against workplace-related cognitive impairment — in other words, workers with higher educational attainment are better able to compensate even if they do incur cognitive problems.

“Sometimes it feels like there’s very little we can do to prevent cognitive problems later in life,” Sabbath said. “But our study points to something we really can do earlier in life to prevent problems later on.”